1. Field of the Invention
The present invention relates to a technique utilized in the fabrication of microminiature devices and, more particularly, to a method and an apparatus for determining the center of lines whose width or spacing is below the one micron range.
2. Prior Art
Linewidth measurement and the determination of line centers is well known in the integrated circuit industry for process characterization and tool evaluation. In particular, this is valuable in the evaluation of lithography systems or in photoresist or etching processes. However, measurement techniques for use with lines whose width or separation in the submicron range have not been known.
EP-A-0013 325 describes an optical system that is particularly adapted for accurate, nondestructive measurement of surface features encountered in semiconductor manufacturing. A spot of laser light is focussed on the surface of the object and then scanned across the features of interest. Light reflected from the edges and surface of the object is detected by photomultipliers which generate signals with peaks representing the edges. Linewidths or distances are then obtained by computing the location differences between the peaks appearing in the multiplier signals.
PTB-Mitteilungen Forschen+Pruefen, Vol. 95, 1/85, pp. 1-10 discloses the determining of edges on lines having a linewidth in the range of one micron. The edges are determined by two focussed laser beams on the object which beams are illuminated successively. A photo detector receives the light reflected from the edges of the lines and the surfaces of the object and generates an electrical signal. The linewidths are obtained by computing locations of signal peaks created by reflection of the beam on the line edges. This method and apparatus are not suitable for determining lines in the submicron range because the shape and the small distance between the signal peaks increases the measurement error to a high degree. Further, the error is negatively influenced by the signal processing which high frequency errors.
The present invention is intended to remedy these drawbacks and describes a method and an apparatus for determining accurately the width and midpoint of lines in the submicron range in real time.